A canyon is a deep ravine or gorge between land masses or cliffs. A canyon is often carved out by a river that flows in the bottom of the canyon. A similar geographic feature occurs in urban areas as skyscrapers or other buildings imitate cliffs with the streets below running like rivers. These man made topographies are referred to as urban canyons. Urban canyons have been studied for the effects on temperature, wind, and air quality.
In addition, urban canyons may influence radio communication. The propagation of radio waves may be affected by urban canyons. Radio waves may be blocked by buildings. Radio waves may be reflected off buildings and diffracted around buildings, following different paths to the same destination. Thus, delays or artifacts may be introduced in radio communication signals by the urban canyon.
The global positioning system (GPS) and other satellite-based positioning systems are susceptible to delays in radio communication signals. The positioning system receiver receives communication signals and determines the distance to the satellites sending the communication signals based on the speed of the communication signals and the time the communication signals were transmitted. Satellite-based positioning systems become unreliable in urban canyons because communication signals may be blocked or delayed. The delayed signal path of the GPS is due to signal reflections and is termed GPS multi-path.